Synthesis of hydrocarbons



Nov. l, 1949. A. CLARK SYNTHESIS OF HYDROCARBONS Filed sept. 1o, 1945INVENTOR ALFRED CLARK ATTORN EYS Patented Nov. l, 1949 SYNTHESIS GFHYDROCARBONS Alfred Clark, Bartlesville, Okla., asslgnor to PhillipsPetroleum Company, a corporation of Deia- Ware Application September 10,1945, Serial No. 615,349

rand carbon monoxide may be made to react exothermically in the presenceof certain catalysts and under specic reaction conditions to formhydrocarbons and oxygenated compounds. The formation of hydrocarbonshaving more than one carbon atom per molecule, especially thosehydrocarbons boiling within the gasoline range, is favored by relativelylow pressures and low temperatures. In general, the synthesis of hy- 4Claims. (Cl. 26o-449.6)

drocarbons by the hydrogenation of carbon Y monoxide is accomplished inthe presence of a metal chosen from group VIII of the periodic table asa catalyst at pressures below about 500 pounds per square inch gage andat temperatures below about 350 C. The synthesis feed gas comprises amixture of about 2 `moles of hydrogen per mole of carbon monoxide and isprepared by the catalytic conversion of natural gas, steam and carbondioxide. Characteristically, certain reaction conditions are optimum forthe particular metal catalyst being used. Moreover, whether a normallygaseous, liquid or solid hydrocarbon is produced depends upon thereaction conditions, especially temperature. which are used to eect thesynthesis. Accurate control of the reaction conditions and dissipationof excess heat liberated by the exothermic nature of the reaction arenecessary to obtain an optimum yield of the desired product.

When hydrogen and carbon monoxide react to form hydrocarbons, part ofwhich boil in the gasoline range, an amount of heat is evolvedequivalent approximately to one-fifth of the heat oi' combustion of theoriginal reactants converted. The liberation of large quantities of heatduring the course of this reaction has presented a serious obstacle tothe industrial use of this process, since it is essential to maintainthe temperature of reaction within very narrow limits in order to obtainhigh yields of desirable products. Excessive rise in temperature duringthe reaction caused by the liberation of heat results in the formationof methane. g

Both the hydrocarbon product andthe neat oi reaction of carbon monoxideandhydrogen are variable and depend on the catalyst and conditions ofoperation used. The formation of the methylene radical brings about anexothermic heat of reaction of about 48,000 calories per mole ofmethylene formed and is the minimum amount of heat that can be releasedfrom two moles of hydrogen reacting with one mole of carbon monoxide.However, in actual practice, the formation of higher hydrocarbons, suchas by polymerization of methylene, bring about an additional heat ofreaction which results in the liberation of heat exceeding 48,000calories.

The application of thermodynamic principles to the hydrogenation ofcarbon monoxide indicates the feasibility of producing thosehydrocarbons boiling within the gasoline range at accurately controlledtemperatures. The approximate linear free energy-temperature relationsfor the synthesis of methane, ethane, normal hexene, normal hexane, andnormal octane, are illustrated by the following over-all equations forreactions occurring in the gas phase with nickel or cobalt catalysts.These equations are represented graphically in The Chemistry ofPetroleum Derivates by Carleton Ellis, vol. II; 1934, page 1226.

The production of hydrocarbons from carbon monoxide and hydrogen isfavored thermodynamically, as is evident from the large negative valuesof the standard free energy change for the over-al1 reactions. In theseries, methane, ethane, normal hexane, and normal octane, the freeenergy change becomes more negative with the sizeof the molecule so thatthe formation of higher members of the series is quite feasible. Atabout 300 C., and atmospheric pressure, it should be possible to obtainany of the paraffin hydrocarbons by reduction of carbon monoxide in thepresence of appropriate catalysts. The validity of this conclusion hasbeen confirmed by the isolation and identification of some of thereaction products which included practically all the members of thealiphatic series from @thans to hectopentacontane (Granma).

bination with external cooling means.

. Under process conditions, `the endothermic` heat requirement in theformation of octanefrom liquid methylalcohol and liquid ethyl alcohol isapproximately 309 B. t. u. and 293 B. t. u., respectively, perV pound ofalcohol; whereas the latent heat of vaporization of liquid methylalcohol and liquid ethyl alcohol is approximately 470 B. t. u. and 370B. t. u., respectively, per pound of alcohol. Even'though some oi `thealcohol decomposes to form hydrocarbons the overall process involving achange from 'a liquid state to a gaseous state and the conversion of thealcohol to hydrocarbons is endothermic. In actual practice thedecomposition and couver sion of alcohol to hydrocarbons is relativelysmall which results in an even larger endothermic heat requirementattributed to the presence of the alcohol than indicated.

Undecomposed alcohol passes through the process and is separated fromthe hydrocarbon product in thel conventional manner, such as byfractional distillation. The alcohol which decomposes is converted tovaluable hydrocarbons composing a portion of the hydrocarbon product. Inthis manner complete utilization oi' the cooling medium is achieved.

Ethylene which may be formed by the dehydration of ethyl alcoholcombines with low-boiling hydrocarbon products to form more desirablehigher boiling hydrocarbons.

The presence of the alcohol does not decrease the eiliciency of thesynthesis catalyst.

In practice, alcohol alone is not used to remove all the excess heat ofreaction 'ing the synthesis process, but alcohol is usually used incomample, a cooling jacket often surrounds the reaction zone throughwhich jacket is passed a suitable fluid medium, such as water, mineralseal oil, etc., to remove the exothermic heat as sensible heat of thefluid.

When using methyl alcohol at least 0.002 pound of alcohol is requiredper B. t. u. of heat to be removed by the vaporization of the alcoholand preferably not more than about 0.003 pound of methyl alcohol per B.t. u. is used. When using ethyl alcohol at least 0.0025 pound of alcoholis required per B. t. u. of heat to be removed by the vaporization ofthe alcohol and preferably not more than about 0.0035 of ethyl alcoholis used. About 0.003 pound of alcohol per B. t. u. of heat removed isusually adequate for alcohols in general. A mixture of methyl and ethylalcohol or other alcohols may be used, and in some cases an inertdiluent, such as hydrocarbons, may be admixed with the alcohol. The useof excessive quantities of alcohol often results in a decrease in thereaction temperature below that required to assure an economical yieldoi product.

In practicing this invention, it is possible to use reaction chambersconsiderably larger in diameter than those normally used in thehydrogenation of carbon monoxide while comparable yields of valuablehydrocarbon products are obtained without the production of abnormalquantities of methane and other undesirable normally gaseoushydrocarbons.

Appropriate catalysts are those which have substantial hydrogenatingpower at low temperatures. Suchcatalysts comprise a metal or compound ofa metal from group VIII of the periodic table, such as iron, cobalt andnickel. Cerium.

For exactas Y pounds per square inch gage;

meng, titanium. zinc, thori and the oxides and other compounds of thesemetals have also been found to possess the necessary charac teristicssuitable for hydrogenating carbon monoxide to'hydrocarbons. Mixtures ofsuch catalysts may be employed or suitable agents or carrlers may beimpregnated with the catalystsl to increase their emciency and strength.The cata,- lysts are usually in a iinely divided form, such as pelletsorgranules Table I below shows the reaction conditions of temperature.pressure, and space velocity characteristlc oi' some of the variouscatalysts which may be used in effecting the synthesis of hydrocarbonshaving more than one carbon atom per molecule.

A TABLE I Preferred ranges of 4operation of some common variouscatalysts which may be used to effect aV synthesis of hydrocarbons isbetween about and 400 C.

In carrying out theprocess of this invention,

pressures ranging from sub-atmospheric to as high as about 2000 poundsper square inch gage may be used, but the preferred range is from about50 to about 500 pounds per square inch gage, more particularly fromabout 100 to about Space velocities may be varied over a considerablerange from low velocities of approximately 80 cubic feet per cubic footoi' catalyst per hour such as are usednormally over cobalt catalyst, upto about 400 or even as high as 30,000 cubic feet per cubic foot ofcatalyst per hour, such as are used over the sintered iron catalysts.These values represent the extremes in space velocities which may beused in carrying out this invention. Space velocity may be defined asvolum'es of gas at standard conditions of temperature and pressure pervolume of catalyst per hour.

The composition oi' the synthesis feed gasis normally in a molar ratioof hydrogen to carbon monoxide between about 3 to 1 and about 1:1,however, for optimum yield oi' normally liquid hydrocarbons a ratiobetween about 2:1 and about 3:2 is preferred.

y Unon use the catalyst may decrease in activity as the result ofdeposition of carbonaceous deposits thereon. Regeneration of thecatalysts may be eiIected in conventional manner, such. as by treatmentwith hydrogen at elevated temperatures.

By the process of this invention higher yields have beenobserved thanobtained by conventional methods. Of the total hydrocarbon product. thenormally liquid hydrocarbons constituted as high as about '15% byweight.

The drawing diagrammatic'ally represents apatascos 2 paratus for a.typical process for the synthesis of hydrocarbons in which an embodimentof the present invention is applicable.

In order that this invention may be more clearly understood and itsapplicability realized, a brief description of a typical process for thesynthesis of hydrocarbons will be recited. Natural gas containingmethane, steam and carbon dioxide obtained from suitable sources areintroduced into reactor t through lines 5, 5 and l, respectively.Hydrogen and carbon monoxide are formed in reactor il in the presence ofa suitable catalyst at approximately atmospheric pressure and at atemperature between vabout 700 and about 800 C. The euent from reactor 0contains hydrogen and carbon monoxide in a molar ratio of about 2: 1,and about 0.5 to about 1.0 mole per cent impurities, such as sulfur.

From reactor d, the euent passes to sulfur removal unit i2 by line e andthrough cooler it. Both inorganic and organic sulfur are removed fromthe eillue-nt in unit i2 by conventional methods known in the art.Inorganic sulfur may be removed by solvent extraction with an aminesolution. Organic sulfur compounds are decomposed in the presence of asuitable catalyst, such as a copper oxide-lead chromate combination, atan elevated temperature of about 400 C. The resulting hydrogen sulfidefrom the decomposition is removed by solvent extraction. The puriedeilluent of hydrogen and carbon monoxide is then passed to heater I t byline l5 and thence to reactor i0 by line IE.

In reactor I8, hydrocarbons are synthesized under reaction conditionssimilar to those previously described and in the Presence of a suitablecatalyst, such as sintered iron, cobalt-thoria, etc. A portion of theexothermic heat of reaction is removed by the vaporization of liquidalcohol introduced into reactor I6 through lines I1, I8 and I9; themajor portion of the alcohol is added through line I8. The remainingexcess heat of reaction above that required to maintain the desiredreaction temperature at about 225 C. is removed by an external coolingmedium passing through lines and 2| counter-currently to the ilow ofgases ln reactor I6. Reactor I6 contains a suitable catalyst for thesynthesis of hydrocarbons, as previously discussed and shown in Table I.

From reactor I6 a vaporous eilluent containing hydrocarbons and alcoholis passed via line 22 to cooler 24 where partial condensation iseiected, and the condensate is collected in accumulator 25 anddischarged therefrom through line 26. A portion of the eiluent may berecycled to reactor l5 via line 23, if desired. This condensatecomprises heavy hydrocarbons and waxes. The temperature of the eilluentgases leaving reactor IB is about 235 C. and cooling the gases to about150 C. is suiiicient to accomplish the degree of partial condensationdesired in accumulator 25. The uncondensed gases from accumulator 25 arepassed through line 21 to cooling tower 28 wherein the gases arecondensed by a spray of water which cools them to about 25 C. Water,liquid hydrocarbons and alcohol are withdrawn from tower 28 through line29 and are passed to settler 3i for a. liquid phase separation betweenhydrocarbons and water containing alcohol dissolved therein.

Uncondensed gases leave settler 3| through line 32 and pas's to mineralseal oil absorber 33. Recovery of propane. butane and heavierhydrocarbons is eflected in absorber 33 by absorption of thesehydrocarbons in mineral seal cil in the conventional manner. Thehydrocarbon-rich mina eral seal oil is withdrawn from the lower portionof absorber Se and passed to a stripping column ed via line 236i. Thelight hydrocarbons, such as propane, butano, etc., are stripped from themineral seal oil by lowering the pressure or heating in stripping column3d. Recovered hydrocarbons from stripping column 35 are passed via line3Q and condenser Se to accumulator fil. mineral seal oil is recirculatedto absorber 33 by means of line 32. Light gases such as hydrogen,methane, and carbon monoxide, are removed from absorber 33 through linei8 and discarded or used as fuel, if desired. These gases may also bepassed to a second and smaller reactor (not shown) for the conversion ofthe remaining hydrogen and carbon monoxide to hydrocarbons.

Liquid hydrocarbons from settler di and accumulator il are passed vialines de, @l and l0 to fractionation unit de wherein desired productsare separated and recovered. Light gases are withdrawn fromfractionation unit i9 through line 5i. Hydrocarbons boiling within thegasoline range are withdrawn through line 52, and heavier hydrocarbonsare removed by line 53.

The aqueous phase in settler 3l is withdrawn by line 55 for the recoveryof alcohol therefrom. The aqueous phase is passed to fractionator lilthrough line 56. In fractionator 57 alcohol is separated and removedthrough line 59. Water is removed as a bottom product through line 58.The alcohol may be recycled, if desired, to reactor It through line 80.

EXAMPLE I A synthesis gas comprising two moles of hydrogen per mole ofcarbon monoxide is reacted to form normally liquid hydrocarbons at atemperature of about 225 C. and about 100 pounds per square inch gage inthe presence of a cobaltthoria synthesis catalyst. The exothermic heatof reaction is removed and the temperature maintained constant partiallyby passing mineral seal oil around the reaction chamber. Heat notremoved by the mineral seal oil is absorbed by introducing liquid methylalcohol into the reaction chamber adjacent to the entering gas.Approximately half of the heat of reaction is removed by the mineralseal oil. In order to hold the temperature substantially constant at 225C., about 6.5 pounds of alcohol per pound of normally liquid hydrocarbonformed is introduced into the reaction chamber. The eilluent iscondensed, and the components separated therefrom, including the alcoholwhich is recycled to the reaction chamber. The hydrocarbon fractionlanalyzed about 'l5 per cent or more normally liquid hydrocarbons.

EXAMPLE II Under similar conditions of operation to those in Example I,ethyl alcohol is used to absorb the heat of reaction to maintain asubstantially constant temperature in the reaction zone. Approximatelyhalf of the excess heat of reaction above that required to maintain thereactants at the desired temperature is removed by external cooling,while the remainder is removed by introducing alcohol into the reactionchamber. About 7.5 pounds of liquid alcohol per pound of normally liquidhydrocarbons formed is introduced into the reaction chamber. Afterseparation, the hydrocarbon fraction analyzes about '75 per cent or morenormally liquid hydrocarbons.

The 4present invention may be varied widely and Stripped variousmodiiications will become apparent to those skilled in the art withoutdeparting from the scope thereof. y r

I claim: A 1. A process for the synthesis of hydrocarbons having morethan one carbon atom per molecule which comprises passing a gaseousmixture comprising hydrogen and .carbon monoxide through a reaction zonein the presence of a synthesis catalyst, maintaining the molar ratio ofhydrogen to carbon monoxide in said gaseous mixture between 2:1 and 3:2,maintaining a pressure in said reaction zone between 15 and 500 p. s. i.g., maintaining a temperature in said reaction zone between 150" and 400C., maintaining a space velocity of gases in said reaction zone between100 and 400, introducing into and vaporizing a liquid monohydric alcoholof from 1 to 5 carbon atoms per molecule in said reaction zone in anamount in the range of 0.002 to 0.0035 pound per B. t. u. of heatremoved from said reaction zone by the alcohol so as to control thetemperature therein and convert a portion of said alcohol to saidhydrocarbons, withdrawing an eiiluent from said reaction zone containinghydrocarbons, recoverlng hydrocarbons from said eiiiuent as a product of.the process, separating unreacted alcohol from said eiiluent, andrecycling the same to said reaction zone as a coolant in the process.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,984,380 Odell Dec. 18, 19342,161,974 Peck June 13, 1939 2,167,004 Pier et al. July 25, 19392,244,196 Herbert June 3, 1941 v2,247,087 Herbert June 24, 19412,406,851 Redcay Sept. 3, 1946 2,417,164 Huber, Jr. Mar. 11, 1947 OTHERREFERENCES Hurd, The Pyrolysis of Carbon Compounds, pages 148, 149, TheChemical Catalog Company 1929.

